In recent years, various proposals for further improving the utilization efficiency of light and saving energy in an optical element such as displays, a light-emitting diode, and a solar cell have been done. For example, in a liquid crystal display, it is known to raise an aperture ratio of the display device by forming a planarization film on a TFT element by application, followed by forming a pixel electrode on the planarization film (see the patent document 1 below). In an organic EL device, it is also known to raise an aperture ratio thereof like the liquid crystal display by the adoption of a method, wherein emission light from a luminous layer which is formed on a transparent pixel electrode on a planarization layer provided on a TFT element by application is taken out from the opposite side of the TFT element, to be called a top emission method, instead of a method wherein emission light from a luminous layer which is formed by deposition on a transparent pixel electrode provided on a substrate is taken out from the side of the substrate, to be called a bottom emission method (see the patent document 2 below).
Furthermore, accompanying to an improved resolution, increasing in size, increasing in the picture quality, and the 3D indication of a display, delay in signals on wiring becomes a problem. Incoming signals to a TFT becomes shorter by increasing of a writing speed of the image data (frame frequency) but there is a limit to extension of the line-width for lowering a wiring resistance. Because of this, it was proposed to resolve the problem of the signal delay by increasing the thickness of wiring (see the non-patent document 1 below).
As materials for these planarization films of a TFT substrate, there are known materials containing an acrylic resin and a quinonediazide compound (see the patent documents 3 and 4 below). Though material properties of these materials, however, do not deteriorate sharply at a high temperature such as 200° C. or more, the decomposition thereof begins gradually at a high temperature such as 230° C. or more and there occurs problems such as lowering of the film thickness and transmittance deteriorations due to coloring of the transparent layer by a high temperature processing of the substrate. Particularly, these materials cannot be used in a process for forming a film on a layer of these materials at a high temperature, which is used in forming devices such as PE-CVD. In addition, these materials are not a best material for using in an organic EL element as decomposition products thereof affect badly to a luminescent efficient and life of an organic EL element. Furthermore, acrylic materials to which a heat resistance is given have a high dielectric constant generally. These materials, therefore, have problems that the electricity consumption becomes larger due to the increase in the parasitic capacitance or the picture quality decreases due to delay of a driving signal in a liquid crystal element. When an insulate material with a large dielectric constant is used, the capacitance can be made smaller by, for example, making a film layer thicker. However formation of a coated film with a uniform film thickness by these materials is difficult generally. In addition, the amount of materials used becomes larger. These materials, therefore, are not preferred.
Polysiloxanes, in particular a silsesquioxane is known as a high transparent material with a high thermal resistance. Though a silsesquioxane is a polymer constructed by a 3-functional siloxane structure unit: Si(O1.5) and is a middle existence of an inorganic silica (SiO2) and an organic silicone (R2SiO) on the chemical structure, the polysiloxane is a singular compound as the compound is soluble in an organic solvent but a cured polysiloxane shows a high thermal resistance which is characteristics of an inorganic silica. When the polysiloxanes are used as a component of a photosensitive composition, it is needed that these are dissoluble in developers such as a tetramethylammonium hydroxide (TMAH) aqueous solution. Therefore, there are proposed a photosensitive composition comprising an acrylic copolymer copolymerized with a silsesquioxane compound in which an acrylic group is given to a particular caged silsesquioxane, an unsaturated carboxylic acid, an unsaturated compound containing an epoxy group and an olefin unsaturated compound, and a quinonediazide compound (see the patent document 5 below), and so on. As the composition comprising complicated systems contains a large amount of organic compounds except for the polysiloxane and a cured material thereof has an insufficient a thermal resistance due to the thermal deterioration of the organic compounds, the composition has problems of coloration and gas generation due to decomposition of the organic compounds and these problems cannot be ignored.
As a photosensitive composition, there is proposed, for example, a photosensitive composition comprising a polysiloxane which is insoluble in a developer, a polysiloxane which is soluble in a developer, and a quinonediazide compound and does not contain other reactive compounds except two kinds of polysiloxanes combined (see the patent document 6 below).
When a material consisting of only a polysiloxane and a quinonediazide compound is cured thermally, the cross-linkage and higher molecular weight formation occur by dehydration and condensation of silanol groups in the polysiloxane. In this thermal curing process, there must be prevented a ‘pattern’ sagging, that is, hole or line patterns obtained by the development flow due to a melt of a film by a low viscosity formation at a high temperature before sufficient proceeding of the thermal pattern curing to decrease the resolution of the patterns. From the patent document 6, it is necessary to raise the molecular weight of the siloxanes sufficiently for preventing the ‘pattern’ sagging. The photosensitive composition, therefore, has a low sensitivity and higher energy is needed for exposure. Further, the composition has faults such that the residual layer thickness thereof is not enough and the material loss is large.